1. Field of the Invention
The present invention generally relates to an image forming apparatus such as a wet electrophotographic printer using a liquid developer. More particularly, the present invention relates to a sludge prevention apparatus in an image forming apparatus for preventing developer sludge from being deposited in a tube member, through which the liquid developer is discharged from and/or flown into an ink cartridge and/or a developing apparatus at the time of developing, thereby preventing the tube member from being blocked.
2. Description of the Related Art
In general, developer feeding apparatuses for use in an image forming apparatus such as a wet electrophotographic printer are classified as either an integral type or a separate type. The integral type developer feeding apparatus is one in which a developer cartridge and a developing apparatus are integrally formed with each other. The separate type developer feeding apparatus is one in which a developer cartridge and a developing apparatus are separately formed and interconnected with each other through a connection tube.
A separate type developer feeding apparatus typically feeds liquid developer made from a mixture of powdered toner and volatile liquid carrier from a developer cartridge into a developing apparatus using a developer feeding pump at the time of developing. The developer is then retrieved from the developing apparatus to the developer cartridge using a developer retrieving pump.
Referring to FIG. 1, a conventional wet electrophotographic printer 10 is schematically shown, which employs a separate type developer feeding system.
The wet electrophotographic printer 10 includes an image forming unit 11 and a developer feeding unit 21.
The image forming unit 11 comprises a photoconductor 1, such as an OPC (Organic PhotoConductive) drum, a laser scanning unit 33, an electrifying section 6, an electric discharge section 7, a developing apparatus 26, and a cleaning blade 8. These components cooperate with each other to perform image forming procedures such as electrification, electric discharge, exposure, and development in sequence, to form a desired image on the photoconductor.
The developing apparatus 26 includes a developing chamber 27 for holding liquid developer 48, a developing roller 2 located under the photoconductor 1, and a deposit roller 5 for forming a layer of electrified developer on the developing roller 2 by applying electric force to the liquid developer 48. The developing apparatus 26 further includes a metering roller 3 for controlling the electrified developer layer formed on the developing roller 2 by the deposit roller 5 to contain a predetermined amount or content (% solid) of toner, and for also feeding the developer layer to the nip between the developing roller 2 and the photoconductor 1. A cleaning roller 4 for cleaning the developing roller 2, and a retrieving chamber 28 for holding or retaining the liquid developer 48 that overflows from the developing chamber 27 is also included in the developing apparatus 26.
In order to feed the liquid developer 48 to the developing chamber 27, there is provided a developer feeding unit 21 above the developing apparatus 26.
The developer feeding unit 21 includes a developer cartridge 15 that comprises a developer storage chamber with a first developer inlet section 16 and a first developer outlet section 17, and a developer feeding pump 18 located between a first and second connection tubes 22 and 23, and wherein the first connection tube 22 is connected to the first developer outlet section 17 of the developer cartridge 15 and wherein the second connection tube 23 is connected to a second developer inlet section 13 of the developing chamber 27 The developer feeding unit 21 further includes a developer retrieving pump 19 located between third and fourth connection tubes 24 and 20 and wherein the third connection tube 24 is connected to the first developer inlet section 16 of the developer cartridge 15 and a wherein the fourth connection tube 20 is connected to a second developer outlet section 14 of the developer retrieving chamber 28.
The developer feeding pump 18 and the developer retrieving pump 19 each include a DC motor (not shown), which is controlled to rotate at a predetermined velocity according first and second control signals PWM1 and PWM2 generated in a controller 29.
Because the conventional printer 10 configured as described above uses liquid developer comprised of powdered toner mixed with a volatile liquid carrier, the toner contained in the liquid developer 48 is deposited in the developer cartridge 15, the developing chamber 27 and the retrieving chamber 28 in the form of sludge if the printer is not used for sufficiently long periods of time.
In order to disperse such toner sludge, conventional printers are provided with stirrers 35 (as shown in FIG. 2) for stirring the toner sludge in the developer cartridge 15, the developing chamber 27 and the retrieving chamber 28 (FIG. 2 shows only the stirrer provided in the developer cartridge 15). There is a problem, however, in that such stirrers 35 cannot disperse the sludge that becomes accumulated in narrow gaps such as are present in the developer inlet tube 40 of the first developer outlet section 17 of the developer cartridge 15, the developer outlet port or tube 13′ of the second developer inlet section 13 of the developing chamber 27, and the developer inlet port or tube 14′ of the second developer outlet section 14 of the retrieving chamber 28. The stirrers 35 can readily stir and disperse the sludge accumulated on the bottoms of the developer cartridge 15, the developing chamber 27, and the retrieving chamber 28.
If the toner sludge becomes accumulated in the developer suction (inlet) tube 40 of the first developer outlet section 17 of the developer cartridge 15 without being dispersed, then the developer outlet port 13′ of the second developer inlet section 13, the developer inlet port 14′ of the second developer outlet section 14, the developer inlet tube 40, the developer outlet port 13′, and the developer inlet port 14′ can all become blocked. If the developer feeding pump 18 and the developer retrieving pump 19 operate under this condition, problems arise in that the liquid developer in the developer cartridge 15 is not properly fed to the developing chamber 27 or, conversely, the liquid developer 48 in the retrieving chamber 28 is not properly retrieved from the developer cartridge 15.
If the liquid developer 48 in the developer cartridge 15 is not properly and adequately fed to the developing chamber, the wet electrophotographic images may not be formed in the developing apparatus 26 due to the shortage of developer. In addition, if the liquid developer 48 in the retrieving chamber 27 is not properly or adequately retrieved from the developer cartridge 15, there will be a serious problem in that the liquid developer 48 overflows from the retrieving chamber 28 and contaminates the surroundings (such as the interior of the wet electrophotographic printer).